The present invention relates in one aspect to artificial ventilation methods and systems for administering and exhausting gases to a mammal, including methods and systems for use in anesthesia and administration of oxygen to patients, and more particularly to artificial breathing systems capable of controlling carbon dioxide rebreathing. The present invention relates in another aspect to a unilimb inspiratory and expiratory breathing device for use in a breathing circuit, which has one or more tubular conduits detachable at a common interface, the interface optionally providing for control of gas flow and operable connection to different functional devices. The present invention also relates to improved components of assisted ventilation systems and methods for providing same.
Breathing circuits are utilized to conduct inspiratory gases from a source of same, such as from an anesthetic machine, to a patient, and to conduct expiratory gases away from the patient. The gases are conducted through two or more conduits, and, generally, at least a portion of the expiratory gas is recycled to the patient after removal of carbon dioxide. To facilitate description of the prior art and the present invention, the end of a conduit directed toward a patient shall be referred to as the distal end, and the end of a conduit facing or connected to a source of inspiratory gases shall be referred to as the proximal end. Likewise, fittings and terminals at the distal end of the breathing circuit, e.g., connecting to or directed at the patient airway device (i.e., endotracheal tube, laryngeal mask, or face mask), will be referred to as distal fittings or terminals, and fittings and terminals at the proximal end of the breathing circuit will be referred to as proximal fittings and terminals. For further information on breathing systems, and anesthetic and ventilation techniques, see U.S. Pat. No. 3,556,097; U.S. Pat. No. 3,856,051; U.S. Pat. No. 4,007,737; U.S. Pat. No. 4,188,946; U.S. Pat. No. 4,232,667; U.S. Pat. No. 5,284,160; Austrian Patent No. 93,941; Dorsch, J. A. and Dorsch, S. E., Understanding Anesthesia Equipment: Construction, Care And Complications, Williams and Wilkins Co., Baltimore (1974) (particularly chapters 5-7); and Andrews, J. J., xe2x80x9cInhaled Anesthetic Delivery Systems,xe2x80x9d in Anesthesia. Fourth Edition, Miller, Ronald, M. D., Editor, Churchill Livingstone Inc., New York (1986) (particularly pp. 203-207). The text of all documents referenced herein, including documents referenced within referenced documents, is hereby incorporated as if same were reproduced in full below.
U.S. Pat. No. 4,265,235, to Fukunaga, describes a unilimb device of universal application for use in different types of breathing systems, which provides many advantages over prior systems. The Fukunaga system utilizes a space saving coaxial, or tube-within-a-tube, design to provide inspiratory gases and remove expiratory gases. Generally, the inner tube is connected at its proximal end to a source of inspiratory, fresh gas, while the outer tube proximal end is connected to an exhaust port and/or to a carbon dioxide absorber (the latter at least partially exhausts into the inspiratory gas source when used in a circle system). In addition to reducing the size of the breathing apparatus connected to a patient by reducing the number of tubes near the patient, the Fukunaga system has additional benefits, such as serving as an artificial nose (expired air warms and humidifies inspired air as the opposing two flows are co-axial in the unilimb device). The Fukunaga circuit is also safer than prior co-axial systems, since the distal end of the inner tube is not connected to the outer tube at a distal fitting, so that the outer tube can be axially extended with respect to the inner tube without disconnecting the proximal end of the inner tube from the source of inspiratory gases; this safety feature can also be used to increase the dead space between the distal ends of the inner tube and outer tube, and thereby allow for adjustment of the amount of expiratory air the patient rebreaths. Dead space is defined herein as the part of the breathing circuit external to the patient which, at the end of expiration, is filled with exhaled gases to be inhaled at the next breath (generally the expired air in the dead space is combined with oxygen and/or other gases provided from a source thereof). It will be appreciated that most known breathing circuits provide a certain amount of dead space when being used. For example, in the device shown in Leagre et al., U.S. Pat. No. 5,404,873, the portion of the breathing circuit that is distal to the end to the inspiratory tube. plus the area between the face mask and the patient""s face all comprises dead space where inspiratory and expiratory gases are mixed. The same is true for the device shown in Leagre, U.S. Pat. No. 5.901,705, except that the dead space also includes the interior volume of the filter.
An embodiment of the Fukunaga unilimb device is commercially manufactured as the UNIVERSAL F(trademark) by King Systems Corporation of Noblesville, Ind., USA. The device includes a proximal terminal comprising a hollow, T-shaped housing with three ports: an inspiratory gas port, an expiratory gas port at a perpendicular angle to the inspiratory gas port, and a third (xe2x80x9cpatientxe2x80x9d) port. The proximal terminal is connected to an outer tube and a coaxial inner tube, which carry gases to and from the proximal terminal. The outer tube is flexible and corrugated, and formed of a transparent (or semi-transparent) material. The proximal end of the outer tube is sealably connected and bonded to the patient port of the proximal terminal. The proximal end of a dark colored, flexible inner tube is scalably connected and bonded to the inspiratory port, and extends through the T-shaped housing, out the patient port, and passes through most of the axial length of the outer tube. The dark color of the inner tube readily permits the user to see through the outer tube to determine whether the inner tube is properly connected.
The inner diameter of the outer tube is sufficiently larger than the outer diameter of the inner tube to permit adequate patient respiration. The distal end of the outer tube is scalably connected and bonded to the exterior of an annular housing which forms a distal terminal. The annular housing of the distal terminal is designed to prevent the distal end of the inner tube from extending beyond the distal end of the outer tube. The entire unit is designed for disposal after a single use.
The UNIVERSAL F(trademark) device offers great advantages over prior dual line and unilimb anesthesia circuits, and respiratory assist devices. However, manufacture of the entire unit requires several complex steps, and must be done with care so that the inner and outer tubes are properly sealed and bonded to the proximal terminal ports at their proximal ends; it is particularly important that the inner tube proximal end be firmly connected to the proximal terminal (at the inspiratory port) when the inner tube carries inspiratory gases, since disconnection during use may not allow sufficient oxygen and/or anesthetic gases to reach a patient, which is highly undesirable.
While U.S. Pat. No. 4,265,235, to Fukunaga, teaches that the tubes and terminals of such a unilimb device can be detachable from one another, in practice, the proximal end of the inner tube is firmly bonded to the inspiratory port, since there remains a risk that the proximal end of the inner tube could be disconnected from the inspiratory port during use if a pressure fit (or friction fit) alone is used. Even if detachment of the inner tube is detected, the design of prior art unilimb devices does not facilitate the reconnection of the inner tube to the inspiratory port of the proximal terminal due to the need to pass the inner tube proximal end through the length of the proximal terminal via the patient port so that it can reach and be connected to the inspiratory port. Thus, the unilimb devices currently used generally comprise a proximal terminal having an integrally connected inner tube and outer tube.
Due to its single-use design, the entire unilimb device, including the distal terminal, proximal terminal, inner tube and outer tube, is disposed of after a single use, along with multiple devices usually connected to the patient nozzle, such as a CO2 monitor (capnometer), temperature and humidity controlling and monitoring devices, an O2 controlling and monitoring device, and an infection controlling device (e.g., a filter). Thus, in addition to the inconvenience of requiring fittings (or a housing accommodating same) for these additional devices at the patient nozzle or distal terminal, replacement of these fittings, tubing, and devices after a single use is expensive, and contributes to ever-growing medical wastes, which are sometimes difficult to find disposal sites for. All of the systems described in the aforementioned patents suffer from similar deficiencies. Therefore, there is a need for an improved unilimb device and ventilation system which reduces costs and helps the environment by reducing waste. There is also a need to simplify the construction, and to increase the safety, efficacy, and reliability of such devices.
Further, it is believed that devices sold for disposal after a single use may sometimes be reused in order to save costs, which may endanger patients. Efforts have been made to make it safer to reuse some patient respiratory conduit components. One problem with this is that the exterior of the patient respiratory conduits, as well as the interior thereof, need to be protected from contamination, so that contaminants from a first patient do not get passed on to subsequent patients by adhering to the exterior of reused components. For example, the device described in Fukunaga U.S. Pat. No. 4,265,235, discussed above, has a coaxial conduit, which can be connected at its distal end (i.e., patient end) to a filter in order to protect the interior of the coaxial conduit from being contaminated. However, the filter does not protect the exterior of the coaxial conduit from contamination. One approach to reducing contamination on the exterior of the conduit is shown in U.S. Pat. No. 5,901,705, to Leagre, in which a sleeve extends proximally from a distal (i.e., patient end) filter over the patient respiratory conduit so that at least the portion thereof nearest the patient is not exposed to contamination from the patient. The device shown in the Leagre ""705 patent places a disposable filter at the patient end of the device. The Leagre device is designed to enable the breathing circuit to be reused on successive patients since the filter and sleeve prevent contamination from entering the breathing circuit from the patient; and prevent contamination in the breathing circuit from entering the patient. Thus the Leagre ""705 patent teaches that the replacement of the relatively inexpensive, one-time-use filter and sleeve between patients permits the relatively more expensive breathing circuit to be used with multiple patients.
Breathing systems generally provide oxygen to a patient, while removing carbon dioxide produced by the patient. For example, in anesthesia, or intensive care, the patient is provided an artificial breathing atmosphere, in which the physician provides a mixture of gases to the patient. In addition to providing oxygen and a variety of vaporized anesthetic agents to the patient, the physician may permit the patient to rebreath some expired gases. Rebreathing simply consists of inhaling gases which have been expired, including carbon dioxide. However, assisted respiration/ventilation to a patient must be safe, and hypoxia (i.e., patient oxygen deficiency) must be avoided. Therefore, inspiratory gases are generally provided at high enough pressure, tidal volume and respiratory rate (hyperventilation) to ensure that hypoxia and atelectasis (lung alveolar collapse) is avoided. Thus, patients are given very high inspired concentrations of oxygen to avoid hypoxia, but unfortunately they often experience abnormally low carbon dioxide levels (i.e., hypocarbia or hypocapnia), and insufficient carbon dioxide can have a negative impact on vital organs (e.g., brain, heart, splanchnic organs, etc.). However, many physicians believe that increasing arterial carbon dioxide partial pressure (PaCO2, also referred to as arterial carbon dioxide tension, often reported as mmHg) in patients by increasing the carbon dioxide breathed by the patient (e.g., by increasing the amount of rebreathing) would cause hypoxia. Thus, it was believed that hypercapnia during assisted ventilation was harmful, since it was believed it would be associated with hypoxia. Further, hypocapnia, while it can be harmful, was believed to be less harmful than hypoxia. Therefore, there remains a need for an improved artificial ventilation method which controls or avoids hypocapnia without compromising vital organ tissue perfusion or oxygenation (i.e., avoids hypoxia).
Further, there is a need to increase safety of assisted ventilation systems by reducing the possibility of component disconnections during use, a need to increase the likelihood that components provided for single-use only are not reused, and that devices, such as filters, meet minimum standards to be used in assisted ventilation systems (as used herein, the terms assisted ventilation system and/or artificial ventilation system refer to any device which provides inspiratory gases to a patient and/or receives expiratory gases from a patient, such as but not limited to anesthesia machines, artificial ventilators, etc.).
The present invention provides in one aspect an improved assisted or artificial ventilation system utilizing a unilimb device for providing and exhausting gases from a mammal, and, in another aspect, an artificial ventilation method which avoids hypocapnia and hypoxia. Further aspects of the present invention include new and improved devices for use in the ventilation methods and systems of the present invention.
Aspects of the present invention relate to the surprising discovery by the inventor that concerns about disconnection of the inner respiratory tube, when connected to the inspiratory port of a proximal terminal in breathing circuits utilizing a unilimb device, such as the UNIVERSAL F(trademark) circuit or the xe2x80x9cBainxe2x80x9d circuit (U.S. Pat. No. 3,856,051), can be eliminated by the new proximal terminal construction of the present invention, which facilitates the use of tubing which is intentionally made to be readily attachable and detachable to the proximal terminal ports, rather than permanently sealably connected as in present systems, and yet provide improved function, safety, and serviceability. The breathing circuit manufacturing process is greatly simplified by eliminating the steps of sealably bonding the proximal ends of the inner and outer flexible respiratory tubes to the inspiratory and patient ports, respectively, of the unilimb proximal terminal. The new unilimb proximal terminal of the present invention facilitates the attachment and detachment of respiratory tubing to the proximal terminal, thus resulting in a cheaper and safer breathing circuit. The new unilimb proximal terminal also permits more efficient placement and utilization of the other breathing circuit components in a multifunctional interface incorporating the unilimb proximal terminal. In another aspect of the present invention, an improved coaxial tube device is provided, which is readily attachable and detachable from the new proximal terminal. The improved coaxial tube device has an inner tube in fixed spaced coaxial parallel relationship to an outer tube at its proximal end, such that a single step is required to connect both tubes to the proximal terminal. This is made possible by a fitting within or at the proximal ends of the coaxial inner and outer tubes, which still permits the distal end of the inner tube to axially move with respect to the distal end of the outer tube. As used herein, coaxial refers to the fact that one tube is contained within the other, but the central axis of both tubes need not be aligned.
Aspects of the present invention involve the surprising discovery by the inventor that hypoxia can be avoided while simultaneously creating intentional dead space in the breathing circuit, thereby increasing rebreathing of expired carbon dioxide, which enables maintenance of normal levels of arterial blood carbon dioxide (i.e., normocapnia) during artificial ventilation. Even more surprising is the discovery by the inventor that moderate hypercapnia will not cause hypoxia, provided sufficient oxygen reaches the patient; in fact, moderate hypercapnia can be beneficial to a patient (e.g., improve cardiovascular oxygen availability and tissue oxygenation). In yet another aspect of the present invention, the arterial blood carbon dioxide tension (PaCO2) can be predictably controlled via a predetermined dead space created in the unilimb device breathing tubes (i.e., the volume in the outer tube defined by the space between the outer tube distal end and the inner tube distal end). The dead space volume may be made adjustable by use of axially extendable and compressible corrugated tubing (which does not rebound to its prior length and maintains its approximate internal diameter despite bending and/or axial length changes): the tubing connects at its proximal end to the patient port of the proximal terminal, and may have dead space calibration markings thereon to permit determination and adjustment of dead space volume contained therein.
In another aspect, the present invention includes an artificial ventilation method which avoids hypocapnia and hypoxia. The method comprises provision of artificial ventilation to a mammal (in which the mammal inspires and expires spontaneously or with mechanical assistance) sufficient to prevent hypoxia, while permitting a sufficient portion of the mammal""s expiratory gases to be rebreathed to allow the arterial carbon dioxide tension of the mammal to be between about 35 mmHg to about 45 mmHg (i.e., normocapnia for a human). In another aspect, the mammal""s expiratory gases are rebreathed sufficiently to permit the arterial carbon dioxide tension to be between about 45 mmHg to about 95 mmHg (i.e., moderate hypercapnia). This surprising invention includes new artificial ventilation tubing and/or filters, and methods for providing same, which permits the user to provide sufficient oxygenation and carbon dioxide to a patient, while using a minimum amount of disposable, single-use materials.
Another aspect of the present invention includes an improved unilimb device useful in providing the above artificial ventilation method. In a preferred embodiment, a unilimb device for use in a breathing circuit includes an outer tube, and an inner tube, each having a proximal end and a distal end. The outer diameter of the inner tube is smaller than the inner diameter of the outer tube, wherein the outer tube can be operably connected at its distal end to a fitting (e.g., endotracheal tube or mask) that can provide artificial ventilation to a mammal. The inner tube is at least partially disposed within the outer tube, and the distal end of the inner tube is disposed within and in direct fluid communication with the outer tube. The proximal end of one of the tubes is connected to an inspiratory gas input (preferably the inner tube), and the proximal end of the other tube is connected to an exhaust outlet. The distal end of the inner tube is axially disposed at a predetermined distance from the distal end of the outer tube to create a dead space in the outer tube between the tube distal ends. The dead space permits the mixing of inspiratory (fresh) gases with expiratory gases from a patient operably connected to the device, and thereby the amount of gases rebreathed by a patient can be related to the dead space volume. This dead space can be predetermined and adjusted to provide for normocapnia or moderate hypercapnia while avoiding hypoxia. In a preferred embodiment, an inner tube and outer tube are provided, which, when operably connected to a mammal to provide respiration, the dead space external of the patient is at least 10 cubic centimeters, and in another preferred embodiment at least 30 cubic centimeters. This dead space may be as small as 10 cubic centimeters for normocarbia in a small mammal (e.g., a human infant), and may exceed 150 cubic centimeters in larger mammals (e.g., adult humans). As used herein, and as is conventionally understood, dead space may also be defined as that volume in a patient respiratory conduit external of a patient and distal of the most distal source in or connected to the patient respiratory conduit of fresh inspiratory gases to the patient, and includes the space in the conduit(s) and devices external of the patient; for example, if a single patient respiratory conduit carries inspiratory and expiratory gases, dead space is the volume in the patient respiratory conduit between the patient and the inspiratory gas inlet, and any filters or other devices therebetween. If, for example, a coaxial patient respiratory conduit is used (which, for example, has an outer flexible conduit for carrying expiratory gases from a patient operably connected to the distal end thereof), and the inner flexible tube of the coaxial patient respiratory conduit is connected to an inspiratory gas inlet, then the volume in the patient respiratory conduit (and any fittings, filters and other devices) between the patient and the distal end of inner flexible tube is dead space.
Since it is desirable to have the assisted ventilation system at a distance from the patient to permit health care personnel better access to the patient, in one embodiment of the present invention, the coaxial tubing is of considerable length, and has little or substantially no dead space therein; the distal end of the inner flexible tube is biased against or bonded to a distal fitting connected to the end of the distal end of the outer flexible tube. A dead space tube can be operably connected to the distal end of the coaxial flexible tubing; in a preferred embodiment, the dead space tube is connected to a distal fitting at the end of the coaxial tubing. The dead space tube can be operably connected through a filter (having a predetermined dead space therein) at its proximal end to the distal fitting at the distal end of the coaxial tubing (thus filtering both inspiratory and expiratory gases), or the filter may be connected at the distal end of the dead space tube. Thus, a coaxial flow of inspiratory and expiratory gases may be directed through a single filter and dead space tube. in another embodiment, the inner tube of the coaxial conduit is of a fixed length and preferably of a dark color (or has a dark colored band about its distal end); the outer tube can have its length adjusted, and is made of a clear (transparent or semi-contraction of the outer tube to alter the axial distance between the distal end of the outer tube and the distal end of the inner tube. The outer tube can be formed of a section of corrugated tubing, such as for example FLEXITUBE(copyright), which upon axial extension from its compressed axial conformation, or vice versa, will retain its axial length (e.g., will not rebound; i.e., accordion-like pleated tubing). Further, the FLEXITUBE(copyright), when bent, will retain the angle of curvature it is bent to without substantial reduction in the tube""s inner diameter. (Suitable corrugated tubing for use in the present invention is used in the Ultra-Flex circuit from King Systems Corporation, of Noblesville, Ind., U.S.A.). The inner tube can be seen through the outer tube and, in one embodiment, the dead space volume can be determined by reference to calibration markings, which are on the outer tube, aligned with the distal end of the inner tube. By placement of a biological contamination filter between the distal ends of the inner and outer tubes and the patient port of the proximal terminal of the unilimb device, the current invention makes it possible to safely extend the service life of the proximal terminal beyond a single use. An example of suitable prior art biological contamination filter means, which can be used in some embodiments of the present invention, is the VIROBAC II Mini-Filter by King Systems. Likewise, other adapters and a variety of single use devices, previously connected at the distal or patient fittings, can be reused by connection to the interface at the proximal side of the biological contamination filter. Since the proximal terminal is more complicated to manufacture, this invention permits substantial cost savings by permitting reuse of the proximal terminal and other devices connected thereto, while simultaneously reducing environmental (medical) wastes.
In another embodiment, patient safety is enhanced by provision of unique connector fittings for connecting components of assisted ventilation systems, for example for connecting tubing and filters. For example, a unique proximal connector fitting on a filter matches and connects to a mating fitting on the distal end of either a single or coaxial patient respiratory conduit. The mating fitting on the distal end of a patient respiratory conduit may be provided with a locking device to prevent accidental disconnection. Further, patient respiratory conduits and proximal terminals may also be provided with a blocking device to prevent an unmatched dead space tube, filter, or other devices from being connected thereto. Thus, for example, only filters meeting minimum requirements can be connected to single or coaxial patient respiratory conduit having a mating fitting. In addition to filters, other devices may be provided with unique connector fittings corresponding to the unique fittings on the distal end of the patient respiratory conduit. In another embodiment of the present invention, an adaptor is provided, in which the distal end has a standard patient device connector to accommodate standard filters and patient airway devices (e.g., endotracheal tube proximal end), and the proximal end has a unique connector fitting for a mating connector on the distal end of a patient respiratory conduit.
In yet another aspect, the present invention includes a system for use in mammals to provide respiratory and other gases. The system comprises a first breathing conduit having a proximal end and a distal end for providing and exhausting respiratory gases from a mammal. and an interface comprising a breathing circuit operably connected to the proximal end of the first breathing conduit. A biological contamination filter blocks biological contaminants in the first breathing conduit from communicating with the interlace components while allowing for adequate transmission of inspiratory and expiratory flows.
The biological contamination filter can be located within the proximal end of the first breathing conduit, or serve as a separate detachable component. In one embodiment of the present invention, a coaxial filter apparatus is provided. The filter apparatus comprises an inner housing having openings at its opposite ends; at least one of the openings has an internal diameter which equals the internal diameter of the inner tube of the breathing conduit, so that the filter device may be attached in a coaxial fashion with the inner tube of the breathing conduit. The inner diameter of the filter device inner housing expands to form a chamber which accommodates a filter having a predetermined diameter to permit sufficient flow therethrough (i.e., flow resistance is inversely proportional to filter surface area). The inner housing is contained within, and in spaced parallel relationship with, an outer housing which is similar or identical in shape, but of sufficiently greater internal diameter throughout to permit fluid to flow between the outer walls of the inner housing and the inner walls of the outer housing. A single disc shaped filter may be contained within the inner housing and radially extend from within the inner housing chamber lo the outer housing chamber, or a filter in the shape of an annular ring may be disposed about the outer diameter of the inner housing filter chamber and extend to the inner wall of the outer housing chamber. The inner and outer filter housings may each be constructed from two funnel shaped components, a pre-filtration housing and postfiltration housing (which are mirror images of each other). the two components can be assembled together after placing a filter therebetween at the center of the filter chambers to be formed thereby.
A preferred embodiment of the proximal terminal interface comprises a T-shaped housing, having an inspiratory gas input (inspiratory port), an expiratory gas outlet (expiratory port), and a first respiratory (patient) port. The first respiratory port can be placed in fluid communication, through the biological contamination filter, with a first breathing (respiratory) conduit leading to a patient. The inspiratory port of the proximal terminal connects to and is integral with an internal conduit, which passes through the housing of the proximal terminal, so that the distal end of the internal conduit forms a second respiratory port, which terminates within the first respiratory port. The second respiratory port has a smaller diameter than the first respiratory port, so that gases may flow through the first respiratory port and through the space between the exterior wall of the inner conduit and the interior wall of the proximal terminal housing. The new proximal terminal of the present invention permits the ready connection and disconnection of an inner tube of a coaxial respiratory conduit to the inspiratory gas source, since direct sealed fluid communication with the inspiratory port is greatly facilitated by the inner conduit of the new proximal terminal housing. Thus, the prior art difficulties with connection of the inner tube of unilimb devices to the inspiratory port arc eliminated, making it possible to avoid sealably bonding the inner flexible respiratory tube to the inspiratory port of the proximal terminal during manufacture.
It is noted that in preferred embodiments of unilimb ventilation devices, the inner tube carries inspiratory gases from an inspiratory gas source, and the outer tube carries expiratory gases. Generally, it is desired that inspiratory gas flow be laminar, while the expiratory gas flow should be turbulent. Turbulent expiratory gas flow is facilitated by the annular shape of the passage between the inner wall of the outer tube and outer wall of the inner tube, as well as by the confluence of gases exiting from the inner tube distal end into the dead space with expiratory air. Further, filtration of the expiratory gases increases turbulent flow in the outer tube, causing a positive end expiratory pressure (PEEP) effect, which helps to maintain positive pressure in the patient airway (to prevent atelectasis). Thus, the coaxial filter apparatus of one embodiment of the present invention helps create turbulent flow in the expiratory gases, when the outer tube is used as the expiratory gas conduit.
In one embodiment, the first breathing or respiratory conduit includes one tube, referred to herein for simplicity as the outer tube, and has a first (proximal) end and a second (distal) end. The outer tube is connected at its first end through a filter device to the first respiratory port, and has its second, or distal, end directed toward the patient. Both the first and second respiratory ports terminate in and are in fluid communication with the proximal end of the outer tube through one or more biological filters. Thus the first breathing conduit between the patient and the proximal terminal can comprise a single tube, the entire length of which provides a dead space, or mixing chamber for inspiratory and expiratory gases. The first breathing conduit is detachable from the proximal terminal for disposal or sterilization. Use of this system reduces costs and waste, since only the breathing conduit is designed for single use. Another advantage is that the proximal terminal of prior art unilimb devices, such as the UNIVERSAL F(trademark), is no longer disposed of after a single use. and may be a permanent part of the interface.
In one embodiment of the present invention, the respiratory conduit may comprise an outer flexible tube, the length of which can be preselected from various lengths to vary the dead space to a preselected volume. In another embodiment, the outer tube can be axially expandable and compressible (i.e., have accordion-like pleats) to make the dead space adjustable; the dead space can be determined by reference to calibration markings on the outer tube. The calibration markings on the pleated tube may be concealed in the folded pleats, and revealed in opened pleats. The calibration markings may be color-coded bands.
In another aspect of the present invention, the first breathing conduit further comprises an inner flexible tube axially disposed within the outer flexible tube. The inner tube proximal end is connected through a biological contamination filter to the second respiratory port, and the distal end of the inner tube terminates inside of the outer tube. The dead space can be adjusted by adjusting the axial distance between the outer tube distal end and inner tube distal end. In one embodiment, the proximal end of the flexible inner tube and the proximal end of the flexible outer tube are held in spaced parallel coaxial relationship by a rigid fitting, formed of coaxial rigid annuli, a smaller annulus within a larger annulus. which are held in fixed spaced relationship by rigid radial struts extending from the exterior of the inner annulus to the interior of the outer annulus; in one embodiment, the struts do not extend to the ends of the inner annulus to permit a flexible conduit to be connected thereover. In a preferred embodiment, the fitting connects to the distal end of a filter device, which has a threaded or flanged connector at its proximal end to permit secure attachment to, and simple detachment from, the first and second respiratory ports. In a preferred embodiment, the internal conduit of the interface proximal terminal carries inspiratory gases to the second respiratory port, and the outer tube of the interface carries expiratory gases entering from the first respiratory port. The inner and outer tubes may be of predetermined lengths to provide a predetermined dead space, or the outer tube may be of variable length to permit adjustment of the dead space (or an extension added to the outer tube, with the extension having a fixed or adjustable volume or dead space); calibration markings on a clear outer tube may be aligned with the end of the inner tube to determine dead space volume.
The provision of readily accessible first and second respiratory ports in the distal end of the proximal terminal permits biological isolation of the first breathing conduit, whether it comprises only an outer tube connected to the first respiratory port, or a coaxial outer tube and inner tube, which are connected to the first and second respiratory ports, respectively. Thus, only the filter and first breathing conduit need be disposed of (or sterilized) after a single use. The new interface of the present invention permits numerous monitoring and control devices to be included in the interface at the proximal end of the biological filter(s). Various devices contained in detachable modules can be repeatedly utilized with the interface, including devices which were formerly attached to the patient nozzle and disposed of after a single-use. Thus, the new assisted ventilation system of the present invention provides for greatly simplified construction of disposable unilimb single use components, which reduces costs of production and at the same time reduces the quantity of materials requiring replacement after a single use. Further, fewer devices need be crowded about the patient, providing improved surgical safety (less clutter at the patient makes for easier surgical access and safety). Insertion of monitoring and control devices at the proximal, post filtration, end of the breathing system, permits improved control and monitoring of the patients"" respiration with a simpler device.
Therefore, the present invention provides a simpler artificial ventilation system, that is easier and less expensive to construct than prior art systems, is easier, safer and less expensive to use, yet provides improved features. Further, the present invention makes possible safer artificial ventilation by providing means and a method for simultaneously preventing hypoxia and hypocapnia. Further details and advantages of the present invention will be appreciated by reference to the figures and description of exemplary embodiments set forth herein.